This invention relates to alkaline earth fluorophosphate luminescent materials. More particularly it relates to strontium-calcium fluorapatite phosphors activated with manganese and antimony and to fluorescent lamp incorporating these phosphor materials.
U.S. Pat. No. 2,488,733 discloses various alkaline earth halophosphate phosphors. The halophosphate host is described by the formula EQU 3M.sub.3 (PO.sub.4).sub.6 M.sup.1 L.sub.2
where L is a halogen or a mixture of halogens and M and M.sup.1 are either different or identical alkaline earth metals. Specific alkaline earth halophosphate materials disclosed are calcium fluorapatite, calcium fluoro-chlorapatite, calcium chloroapatite, calcium-strontium fluoro-chloroapatite strontium fluorapatite, calcium bromo-chloroapatite, barium fluorapatite, barium fluorochloroapatite and barium chlorapatite. The materials are activated with antimony and manganese. In lieu of antimony, bismuth, tin or lead can be used.
U.S. Pat. No. 2,965,786 discloses that cadmium can be added to halophosphate of the above formula where M and M.sup.1 are calcium.
U.S. Pat. No. 3,549,552 discloses calcium fluorochloroapatite materials which are useful in the production of lamps exhibiting a "daylight" color. "Daylight" is a color defined by an oval that has x values ranging from about 0.307 to about 0.319 and y values ranging from about 0.330 to about 0.345. As defined in the American National Standard Specifications for the Chromaticity of Fluorescent Lamps the objective for daylight is x=0.313, y=0.337.
U.S. Pat No. 4,075,532 discloses the composition defined by the fromula EQU Ca.sub.10-w-x-y Cd.sub.x Sb.sub.y (PO.sub.4).sub.6 F.sub.2-y O.sub.y
wherein
w is from 0 to 0.2 PA0 x is from 0.25 to 0.5 PA0 y is from 0.02 to 0.2 PA0 a is from about 0.25 to about 4.75-w-x-y PA0 w is from 0 to about 0.2 PA0 x is from about 0.05 to about 0.5 PA0 y is from about 0.02 to about 0.2
The chromaticity of the foregoing composition is stated to vary along a line x in FIG. 3 of the above patent. The variation is due to the manganese content. A material having x in the above formula of about 0.03 is stated to have chromaticity coordinates of x=0.409 and y=0.432. The values given take into account the effect of the mercury emission. Manganese at low levels causes the halophosphates to emit a light blue and at higher levels, eg wherein x in the formula given in U.S. Pat. No. 4,075,532 is about 5% of the total phosphor weight, the emission of the phosphors shifts toward the red portion of the spectrum.
When strontium is substituted for all of the calcium in the fluorapatite system and the levels of manganese and antimony are kept constant the emission is shifted toward the green portion of the spectrum.
It is believed, therefore, that new halophosphate compositions that yield chromaticity values that were unexpected from the prior art constitutes an advancement in the art.